Thermal interface materials including polymeric phase-change materials

ABSTRACT

In an example, a thermal interface material includes a polymeric phase-change material.

I. FIELD OF THE DISCLOSURE

The present disclosure relates generally to thermal interface materialsincluding polymeric phase-change materials.

II. BACKGROUND

In modern computers, large amounts of heat are generated within thecentral processing units (CPUs) which must be removed in order tomaximize speed and reliability, to extend product life, and to preventspontaneous failure due to overheating. Heat may be removed from CPUs byattaching an air-cooled heat sink or a liquid-cooled cold plate to thetop of the processor die, with a thermal interface material (TIM) placedbetween the chip die and cooling apparatus to reduce the large thermalcontact resistance that can occur at bare solid-solid surface contacts.Although the use of TIMs is closely associated with electronics thermalmanagement, TIMs may also be used in other engineering or industrialapplication for which minimizing the thermal interface resistancebetween surfaces is desirable.

While some thermal interface materials may be able to reduce the thermalcontact resistance as compared to bare surfaces, the thermal resistanceof the TIM itself may be a significant contributor to the total thermalresistance between the chip and the cooling environment, therebylimiting the amount of heat which can be effectively removed from theprocessor while maintaining the temperature within an acceptable rangeof values. The limit on the amount of heat that can be removed may limitthe power and processing capabilities of the CPU. In some cases,grease-like or paste-like TIMs contain volatile compounds which degradeor can be lost after long-term exposure to the elevated temperaturesassociated with electronics thermal management. Such mass loss and othertypes of TIM “pump out” may leave air voids between the processor andthe cooling apparatus, resulting in the creation of localized regions ofelevated temperature on the processor chip which may lead to prematurefailure.

III. SUMMARY OF THE DISCLOSURE

According to an embodiment, a thermal interface material is disclosedthat includes a polymeric phase-change material.

According to another embodiment, a process of forming a thermalinterface material is disclosed. The process includes forming a mixturethat includes a vinyl-terminated fatty acid monomer having a chemicalformula C₂H₄—R—C(O)OH and an ethylene glycol monomer having a chemicalformula C_(2n)H_(4n+2)O_(n+1). The process also includes polymerizingthe mixture to form a diene and polymerizing the diene to form apolymeric phase-change material. The process further includes forming athermal interface material that includes the polymeric phase-changematerial.

According to another embodiment, an article of manufacture is disclosed.The article of manufacture includes a first component, a secondcomponent, and a thermal interface material. The thermal interfacematerial is disposed between the first component and the secondcomponent and includes a polymeric phase-change material.

One advantage of the present disclosure is the ability to form a thermalinterface material between a heat source and a heat sink that includes apolymeric phase-change material. Another advantage of the presentdisclosure is the ability to form a thermal interface material havingacceptable material properties in a temperature range associated withelectronics thermal management.

Features and other benefits that characterize embodiments are set forthin the claims annexed hereto and forming a further part hereof. However,for a better understanding of the embodiments, and of the advantages andobjectives attained through their use, reference should be made to theDrawings and to the accompanying descriptive matter.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chemical reaction diagram showing the preparation of apolymeric phase-change material for use as a thermal interface material,according to one embodiment;

FIG. 2 is a diagram showing the preparation of a thermal interfacematerial that includes a polymeric phase-change material; and

FIG. 3 is a flow diagram showing a particular embodiment of a process offorming a thermal interface material that includes a polymericphase-change material.

V. DETAILED DESCRIPTION

The present disclosure describes thermal interface materials thatinclude polymeric phase-change materials (i.e., where the polymer itselfit a phase change material, not a phase-change material that is blendedwith the polymer). Other phase change materials that may be used inelectronic applications may be composed of waxes and may suffer frompoor thermal resistance. That is, the thermal resistance increases withincreasing thermal cycles, thereby degrading performance. For example,while such phase change materials may appear to provide the possibilityof improving TIM performance, such phase change materials may have poorthermal stability at relatively moderate temperature (e.g., >70° C.).Metallic TIMs, such as those based on patterned indium, may not be proneto mass loss but may be prohibitively expensive for many applications orunavailable in the future due to a limited raw material supply andincreasing demand for use in other areas of technology.

In the present disclosure, thermal interface materials that includepolymeric phase-change materials as described herein may provide highthermal transport properties, may demonstrate long-term stability withinthe operational temperature range of electronics, and may be composed ofmaterials that are abundant and cost-effective. The polymeric materialsof the present disclosure may have a melting temperature and heat offusion comparable to that of phase change materials based on paraffin orfatty acids yet possessing sufficient thermal stability.

The polymeric phase-change materials of the present disclosure may havea suitably high melting enthalpy to be comparable with wax materials andsalt-based phase-change materials and a melting temperature in atemperature range appropriate for a desired application (e.g., in arange of 0° C. to 100° C., where TIM phase-change materials may be atthe higher end of this range, while insulating materials may be at thelower end of this range). Further, in order to overcome the shortcomingsof wax/metallic TIMs described above, the polymeric phase-changematerials of the present disclosure may have a high thermal stabilityconsistent with what is commonly observed for polymers but uncommon forwaxes and sufficient mechanical integrity typically absent in waxeswhich aids in the incorporation of the polymeric phase-change materialsin structural applications.

Referring to FIG. 1, a chemical reaction diagram 100 illustrates thepreparation of a polymeric phase-change material for use as a thermalinterface material, according to one embodiment. FIG. 1 illustrates thata vinyl-terminated fatty acid monomer and an ethylene glycol monomer maybe polymerized to form a diene, and the diene may be polymerized to forma polymeric phase-change material. As described further herein withrespect to FIG. 2, the polymeric phase-change material formed accordingto the process illustrated in FIG. 1 may be used to form a thermalinterface material having acceptable material properties for aparticular thermal management application, such as electronics thermalmanagement.

FIG. 1 illustrates an example of a process of forming a thermalinterface material including a polymeric phase-change material. Theprocess includes forming a mixture that includes a vinyl-terminatedfatty acid monomer having a chemical formula C₂H₄—R—C(O)OH and anethylene glycol monomer having a chemical formula C_(2n)H_(4n+2)O_(n+1).In FIG. 1, the chain length of the alkyl group (R) between a terminalvinyl group and a carbonyl group of the vinyl-terminated fatty acidmonomer is represented by a first integer value x. Further, a secondinteger value n indicates that the ethylene glycol monomer may includeethylene glycol (where n=1) or a polyethylene glycol (where n≥2).

The first chemical reaction of FIG. 1 illustrates that the mixture maybe polymerized to form a diene (e.g., via an acyclic metathesis (ADMET)polymerization reaction). As described further herein, materialproperties of the polymeric phase-change material (e.g., meltingtemperature, melting enthalpy, etc.) formed from the diene may be“tailored” to a particular thermal management environment (e.g., forelectronic device thermal management) by adjusting a first portion ofthe diene corresponding to the vinyl-terminated fatty acid monomer(represented by the integer x in FIG. 1) and a second portion of thediene corresponding to the ethylene glycol monomer (represented by theinteger n in FIG. 1).

The second chemical reaction of FIG. 1 illustrates that the diene may bepolymerized (e.g., via an ADMET polymerization reaction) to form apolymeric phase-change material. As described further herein withrespect to FIG. 2, a thermal interface material may be formed bydisposing the polymeric phase-change material (e.g., in the form of apolymeric sheet) between a first component (e.g., a heat source, such asa semiconductor die) and a second component (e.g., a heat sink). In somecases, the polymeric sheet (including the polymeric phase-changematerial) may have a first thickness value (e.g., in a range of 8 mm to20 mm). Application of pressure to the polymeric sheet may reduce thefirst thickness value to a second thickness value (e.g., about 1 mm).The polymeric phase-change material may melt and conform to the matingsurfaces (e.g., a surface of the heat source and a surface of the heatsink).

In a particular embodiment, the vinyl-terminated fatty acid monomerillustrated in FIG. 1 may be formed from a bio-renewable material. Toillustrate, in the case of castor oil, the chain length of the alkylgroup (R) between a terminal vinyl group and a carbonyl group of thevinyl-terminated fatty acid monomer (represented by the integer x) maybe 8 carbon atoms. In some cases, a particular vinyl-terminated fattyacid monomer (or combination of monomers) having a particular alkylchain length (e.g., ≥8 carbon atoms) may be selected in order to“tailor” the material properties of the polymeric phase-change materialby adjusting a contribution of the vinyl-terminated fatty acid monomerto an overall chain length of the diene.

In some cases, the ethylene glycol monomer includes ethylene glycol(where n=1). In other cases, the ethylene glycol monomer may include apolyethylene glycol (where n≥2), such as tetraethylene glycol (wheren=4), among other alternatives. In some cases, a particular ethyleneglycol monomer (or combination of monomers) having a particular numberof repeating CH₂—CH₂—O groups (e.g., ≥1 repeating units) may be selectedin order to “tailor” the material properties of the polymericphase-change material by adjusting a contribution of the ethylene glycolmonomer to an overall chain length of the diene.

In some cases, the material properties of the polymeric phase-changematerial may be “tailored” to a particular thermal managementenvironment (e.g., electronic device thermal management) by adjusting acombination of the contribution of the vinyl-terminated fatty acidmonomer and the contribution of the ethylene glycol monomer to anoverall chain length of the diene. As illustrative, non-limitingexamples, acceptable material properties for a thermal interfacematerial disposed between a heat source such as a semiconductor die anda heat sink may include a melting transition temperature (T_(m)) in arange of 0° C. to 100° C., a melting enthalpy in a range of 200 J/g to400 J/g, and a thermal stability parameter (T_(d)) of 5% mass loss (orless) at a temperature that is in a range of 250° C. to 450° C.

Example 1

A first portion of the overall chain length of the diene correspondingto the vinyl-terminated fatty acid monomer is 16 (where x=8) and asecond portion of the overall chain length of the diene corresponding tothe ethylene glycol monomer is 1 (where n=1). The polymeric phase-changematerial formed via polymerization of such a diene has a thermalstability parameter (T_(d)) of 5% mass loss at 390° C., a meltingtransition temperature (T_(m)) of 58° C., and a melting enthalpy of 350J/g.

Example 2

A first portion of the overall chain length of the diene correspondingto the vinyl-terminated fatty acid monomer is 16 (where x=8) and asecond portion of the overall chain length of the diene corresponding tothe ethylene glycol monomer is 4 (where n=4). The polymeric phase-changematerial formed via polymerization of such a diene has a thermalstability parameter (T_(d)) of 5% mass loss at 300° C., a meltingtransition temperature (T_(m)) of 45° C., and a melting enthalpy of 240J/g.

Thus, FIG. 1 illustrates an example of a process of preparing apolymeric phase-change material for use as a thermal interface material.As illustrated and further described herein with respect to FIG. 2, thepolymeric phase-change material formed according to the processillustrated in FIG. 1 may be used to form a thermal interface materialdisposed between a first component (e.g., a heat source, such as asemiconductor die) of an article of manufacture (e.g., an electronicdevice) and a second component (e.g., a heat sink) of the article ofmanufacture.

Referring to FIG. 2, a diagram 200 illustrates the formation of athermal interface material that includes a polymeric phase-changematerial. In FIG. 2, the polymeric phase-change material illustrated inFIG. 1 (e.g., in the form of a polymeric sheet) may be disposed betweentwo components, and pressure may be applied to form an article ofmanufacture having a thermal interface material that includes thepolymeric phase-change material between the two components.

In the example of FIG. 2, the polymeric phase-change material of FIG. 1may be in the form of a polymeric sheet 202 having a first thicknessvalue 204 (identified as “t₁” in FIG. 1). The polymeric sheet 202 may bedisposed between a first component 206 (e.g., a semiconductor die) and asecond component 208 (e.g., a heat sink), and pressure may be applied toform a thermal interface material 210 having a second thickness value212 (identified as “t₂” in FIG. 2) that is less than the first thicknessvalue 204. In a particular embodiment, the first thickness value 204(prior to application of pressure to the polymeric sheet 202) may be ina range of 8 millimeters to 20 millimeters. The polymeric phase-changematerial may melt and conform to a first surface (associated with thefirst component 206) and a second surface (associated with the secondcomponent 208). In a particular embodiment, the second thickness value212 associated with the thermal interface material 210 may be reduced toabout 1 millimeters.

In a particular embodiment, the thermal interface material 210 thatincludes the polymeric phase-change material may have a meltingtransition temperature (T_(m)) in a range of 0° C. to 100° C., a meltingenthalpy in a range of 200 J/g to 400 J/g, and a thermal stabilityparameter (T_(d)) of 5% mass loss at a temperature that is in a range of250° C. to 450° C. As an example, the polymeric phase-change materialmay have a thermal stability parameter (T_(d)) of 5% mass loss at 390°C., a melting transition temperature (T_(m)) of 58° C., and a meltingenthalpy of 350 J/g. As another example, the polymeric phase-changematerial may have a thermal stability parameter (T_(d)) of 5% mass lossat 300° C., a melting transition temperature (T_(m)) of 45° C., and amelting enthalpy of 240 J/g.

Thus, FIG. 2 illustrates an example of a process of forming a thermalinterface material that includes a polymeric phase-change material. Inthe particular embodiment illustrated in FIG. 2, the polymericphase-change material formed according to the process described hereinwith respect to FIG. 1 may be formed into a polymeric sheet and disposedbetween two components (e.g., of an electronic device). The polymericphase-change material may melt and conform to the surfaces of thecomponents. The thermal interface material having the polymericphase-change material may provide acceptable material properties atelevated temperatures associated with electronics thermal management.

Referring to FIG. 3, a flow diagram illustrates a particular embodimentof a process 300 of forming a thermal interface material that includes apolymeric phase-change material. In the example of FIG. 3, the process300 further includes disposing the thermal interface material between afirst component (e.g., a heat source) of an article of manufacture and asecond component (e.g., a heat sink) of the article of manufacture.

In the particular embodiment illustrated in FIG. 3, operationsassociated with an example process of forming a polymeric phase-changematerial are identified as operations 302-306, while operationsassociated with forming a thermal interface material that includes thepolymeric phase-change material are illustrated as operation 308. Itwill be appreciated that the operations shown in FIG. 3 are forillustrative purposes only and that the operations may be performed atalternative times, by a single entity or by multiple entities, or acombination thereof. As an example, one entity (e.g., a specialtychemical manufacturer) may produce the diene, another entity may producethe polymeric phase-change material, while another entity may form apolymeric sheet that includes the polymeric phase-change material.Further, alternative or additional entities (e.g., an electronic devicemanufacturer) may form the thermal interface material that includes thepolymeric phase-change material by disposing the polymeric sheet betweena first component (e.g., a heat source) and a second component (e.g., aheat sink) and applying pressure. The polymer may melt and conform tothe component surfaces.

The process 300 includes forming a mixture that includes avinyl-terminated fatty acid monomer and an ethylene glycol monomer, at302. The vinyl-terminated fatty acid monomer has a chemical formulaC₂H₄—R—C(O)OH, and the ethylene glycol monomer has a chemical formulaC_(2n)H_(4n+2)O_(n+1). For example, referring to FIG. 1, thevinyl-terminated fatty acid monomer shown on the left side of thechemical reaction diagram 100 may be mixed with an ethylene glycolmonomer (e.g., ethylene glycol or a polyethylene glycol, such astetraethylene glycol).

The process 300 includes polymerizing the mixture to form a diene, at304. For example, referring to FIG. 1, the mixture that includes thevinyl-terminated fatty acid monomer and the ethylene glycol monomershown on the left side of the chemical reaction diagram 100 may bepolymerized to form the diene shown on the right side of the chemicalreaction diagram 100. As described further herein, material propertiesof the polymeric phase-change material (e.g., melting temperature,melting enthalpy, etc.) may be “tailored” to a particular thermalmanagement environment (e.g., for electronic device thermal management)by adjusting a first portion of the diene corresponding to thevinyl-terminated fatty acid monomer (represented by the integer x inFIG. 1) and a second portion of the diene corresponding to the ethyleneglycol monomer (represented by the integer n in FIG. 1).

The process 300 includes polymerizing the diene to form a polymericphase-change material, at 306. For example, referring to FIG. 1, thediene shown on the right side of the chemical reaction diagram 100 maybe polymerized to form the polymeric phase-change material shown belowthe diene.

The process 300 includes forming a thermal interface material thatincludes the polymeric phase-change material, at 308. For example,referring to FIG. 2, the thermal interface material 210 that includesthe polymeric phase-change material of FIG. 1 may be formed viaapplication of pressure to the polymeric sheet 202 disposed between thefirst component 206 (e.g., a heat source, such as a semiconductor die)and the second component 208 (e.g., a heat sink).

Thus, FIG. 3 illustrates an example of a process of forming a thermalinterface material that includes a polymeric phase-change material. Asdescribed further herein, the thermal interface material having thepolymeric phase-change material may provide acceptable materialproperties at elevated temperatures associated with electronics thermalmanagement.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the disclosedembodiments. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thescope of the disclosure. Thus, the present disclosure is not intended tobe limited to the embodiments shown herein but is to be accorded thewidest scope possible consistent with the principles and features asdefined by the following claims.

The invention claimed is:
 1. A method of forming a material for thermalmanagement comprising: forming one or more vinyl-terminated fatty acidsfrom a bio-renewable material comprising castor oil; forming a mixturecomprising one or more vinyl-terminated fatty acids and one or moreglycols; polymerizing the mixture to form a diene; polymerizing thediene to form a polymeric phase-change material; and forming a thermalinterface material that includes the polymeric phase-change material. 2.The method of claim 1, wherein the polymeric phase-change material isformed via an acyclic diene metathesis (ADMET) polymerization reaction.3. The method of claim 1, further comprising: disposing the polymericphase-change material between a first component and a second component,the polymeric phase-change material having a first thickness value; andapplying pressure to reduce the first thickness value to a secondthickness value.
 4. The method of claim 3, wherein the first thicknessvalue is in a range of 8 millimeters to 20 millimeters.
 5. The method ofclaim 3, wherein the second thickness value is about 1 millimeters. 6.The method of claim 3, wherein the first component includes asemiconductor die, and wherein the second component includes a heatsink.
 7. The method of claim 1, wherein the one or more glycols includesethylene glycol.
 8. The method of claim 1, wherein the one or moreglycols has the formula C_(2n)H_(4n+2)O_(n+1), and wherein n is aninteger of 2 or more.
 9. The method of claim 8, wherein the one or moreglycols includes tetraethylene glycol.
 10. The method of claim 7,wherein the one or more vinyl-terminated fatty acids has a chemicalformula C₂H₄—R—C(O)OH, and wherein R includes a chain of at least 8carbon atoms between a terminal vinyl group and a carbonyl group of theone or more vinyl-terminated fatty acids.
 11. A method of forming amaterial for thermal management comprising: forming a mixture comprisingone or more vinyl-terminated fatty acids and one or more glycols;polymerizing the mixture to form a diene; polymerizing the diene to forma polymeric phase-change material; and forming a thermal interfacematerial that includes the polymeric phase-change material by (a)disposing the polymeric phase-change material between a first componentand a second component, the polymeric phase-change material having afirst thickness value in a range of 8 millimeters to 20 millimeters; and(b) applying pressure to reduce the first thickness value to a secondthickness value.
 12. The method of claim 11, wherein the secondthickness value is about 1 millimeters.
 13. The method of claim 11,wherein the first component includes a semiconductor die, and whereinthe second component includes a heat sink.
 14. A method of forming amaterial for thermal management comprising: forming a mixture comprisingone or more vinyl-terminated fatty acids and one or more glycolsselected from the group consisting of ethylene glycol and tetraethyleneglycol; polymerizing the mixture to form a diene; polymerizing the dieneto form a polymeric phase-change material; and forming a thermalinterface material that includes the polymeric phase-change material by(a) disposing the polymeric phase-change material between a firstcomponent and a second component, the polymeric phase-change materialhaving a first thickness value in a range of 8 millimeters to 20millimeters; and (b) applying pressure to reduce the first thicknessvalue to a second thickness value.
 15. The method of claim 14, whereinthe one or more vinyl-terminated fatty acids is formed from abio-renewable material.
 16. The method of claim 14, wherein the one ormore vinyl-terminated fatty acids has a chemical formula C₂H₄—R—C(O)OH,and wherein R includes a chain of at least 8 carbon atoms between aterminal vinyl group and a carbonyl group of the one or morevinyl-terminated fatty acids.
 17. The method of claim 14, wherein thefirst component includes a semiconductor die, and wherein the secondcomponent includes a heat sink.